学步园

//poj2190 只有最后一位可以是X 
#include <iostream>
#include <string>
using namespace std;
int toChar(char c)
{
	if(c == 'X')
		return 10;
	return c-'0';
}
int main()
{
	string a;
	getline(cin, a);
	int sum = 0;
	int index = 0;
	bool ok = false;
	for(int i = 0; i < a.length(); i++)
	{
		if(a[i] != '?')
		{
			sum += toChar(a[i]) * (10 - i);
		}
		else
			index = i;
	}
	int i;
	if(index == 9)
	{
		for(i = 0; i <= 10; i++)
		{
			if((sum + (i)*(10-index)) % 11 == 0 )
			{
				ok = true;
				break;
			}
		}
	}
	else
	{
		for(i = 0; i < 10; i++)
		{
			if((sum + (i)*(10-index)) % 11 == 0 )
			{
				ok = true;
				break;
			}
		}
	}
	if(ok)
	{
		if(i == 10)
			cout<<"X"<<endl;
		else
			cout<<i<<endl;
	}
	else
	{
		cout<<-1<<endl;
	}
	return 0;
}